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Physics · 术语表

什么是 Time constant？

Definition 30.6 High School Physics · 第 30 章 — RC and RL Circuits

The time constant of an RC circuit is $\tau = RC$ . Units: $\Omega \times \mathrm{F} = (\mathrm{V}/\mathrm{A})(\mathrm{C}/\mathrm{V}) = \mathrm{C}/\mathrm{A} = \mathrm{s}$ — the circuit’s own tempo.

示例

Example 30.9 (A flash unit’s numbers)

A photo flash charges $C = 800\,\text{µ}\mathrm{F}$ through $R = 1.0\,\mathrm{k}\Omega$ : $\tau = 10^3 \times 8.0\times10^{-4} = 0.80\,\mathrm{s}$ , so the “ready” light — wired to trip at $95\%$ — waits $3\tau \approx 2.4\,\mathrm{s}$ : the whine of the hook. Fired through the flash tube’s mere $0.50\,\Omega$ , the same capacitor empties with $\tau' = 0.40\,\mathrm{ms}$ : two thousand times faster out than in.

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